Fluoropolymers are generally renowned for their chemical and physical inertness. Indeed, their excellent barrier properties and hydrophobic character have been exploited for applications such as, for example, moisture and noxious gas barriers, anti-corrosion coatings, and non-stick coatings. Examples of commonly used fluoropolymers include polytetrafluoroethylene, polyvinylidene difluoride, and copolymers of vinylidene difluoride with tetrafluoroethylene and hexafluoropropylene.
Multilayer constructions in which a fluoropolymeric substrate is bonded to a second non-fluorinated substrate have a variety of industrial applications. Such constructions find utility, for example, in fuel line hoses and related containers, hoses and gaskets for use in chemical processing, and in protective film laminates. However, non-adhesive properties of fluoropolymeric surfaces may make it difficult to obtain sufficient adhesion between layers in such composite articles.
Various conventional approaches have been used to improve adhesion to fluoropolymeric substrates, including modifying the surfaces of such substrates using harsh chemical treatments such as alkali metal reduction (e.g., using alkali metal in liquid ammonia or sodium-naphthalene in glyme), and, in the case of polyvinylidene difluoride, using concentrated alkali metal hydroxide solutions in the presence of a phase transfer catalyst. Other previous methods to improve adhesion to fluoropolymeric surfaces include radiation-processing methods such as laser induced surface modification and photochemical reduction in the presence of an organic electron donor (e.g., a primary, secondary, or tertiary amine).
Each of the above methods for modifying surfaces of fluoropolymeric substrates may have disadvantages such as, for example, cost, the need to use odiferous or noxious chemicals, and/or the formation of colors (e.g., yellow, orange, dark brown) during processing.
It would be desirable to have new methods for modifying surfaces of fluoropolymeric substrates such that they may be bonded to non-fluorinated substrates, especially if they can be practiced relatively inexpensively, without odiferous chemicals, and/or without resulting in excessive color formation.